postfix-relay

Postfix SMTP relay docker image. Useful for sending email without using an external SMTP server.

Usage

docker pull mwader/postfix-relay or clone and build it yourself. Default postfix is configured to be an open relay that rely on docker networking for firewalling. So be careful not to expose it publicly.

All postfix configuration options can be set using POSTFIX_ environment variables. See Dockerfile for default configuration. It will work without making any changes but you might want to set POSTFIX_myhostname, the FQDN used by 220/HELO.

Using docker run

docker run \
	-e POSTFIX_myhostname=smtp.domain.tld \
	--name smtp \
	mwader/postfix-relay

Now run some other container with a link to smtp and use it as SMTP server.

Using docker-compose

app:
  links:
    - smtp
  # use hostname "smtp" as SMTP server

smtp:
  image: mwader/postfix-relay
  restart: always
  environment:
    - POSTFIX_myhostname=smtp.domain.tld

SPF

When sending email using your own SMTP server it is probably a very good idea to setup SPF for the domain your sending mail from.

DKIM

To enable DKIM specifying a white space separated list of domains using OPENDKIM_DOMAINS. At container start new key pairs for each domain will be generated if not found in /etc/opendkim/keys/<domain>". To persist the keys make sure to add a host directory volume for /etc/opendkim/keys. If your using docker-compose it will automatically take care of moving data volumes between container recreates.

DNS records to configure can be found in the container log or by running docker exec -ti <container> sh -c "cat /etc/opendkim/keys/*/mail.txt".

License

postfix-relay is licensed under the MIT license. See LICENSE for the full license text.